Diseases of the heart are the major cause of non-accidental death in people over the age of 65 and are the second most common cause for people aged 45-64. A common form of heart disease is ischemic heart disease, which is caused by blockage, or partial blockage, of blood vessels leading to the heart resulting in slow deterioration and eventual death of heart cells. Although there are several treatments available for ischemic heart disease including angioplasty and bypass surgery, these treatments are unavailable for many patients and, for others, they offer only temporary relief.
One promising treatment is the introduction, via a catheter, of specific medicants directly to the heart and/or related blood vessels, such as angiogenesis-promoting substances or gene therapeutic agents. Catheter delivery has the potential to deliver the therapeutic agent or agents by physically placing them exactly where they are needed. Typically, catheters are introduced into the body via the femoral artery and then directed to the heart or other areas. Catheter delivery requires that the catheter be both flexible so as to bend where necessary to follow the blood vessels or arteries and sufficiently rigid so as to be controllable for accurate targeted agent delivery. What is still needed, however, is a catheter that is both flexible and controllable.
Another form of heart disease is abnormal heart rhythms (cardiac arrhythmias). There are a variety of causes of arrhythmias; for example, cardiac valve disease, ischemic heart disease, and rheumatic heart disease may all cause arrhythmias. The contraction of the heart is governed by electrical signals which originate in the right atrium and then are transmitted throughout the heart creating a coordinated heartbeat. Problems arise when other parts of the heart generate electrical signals which are out of phase with the normal signals or when the transmission of the correct signals is perturbed by defects in the conduction system. These difficulties can be overcome by the selective destruction of abnormal cells that are the origin of the electrical problems. This can be accomplished by chemical agent ablation with appropriate chemical agents delivered to the critical part or parts of the heart by means of a suitable catheter. What is still lacking, however, is a mechanism to administer ablating chemical agents accurately to specific areas of the heart using a catheter.
While catheters are a remarkably efficient devices for delivering various kinds of drugs to the heart and associated blood vessels, there still are disadvantages associated with their use that either restrict the use of catheters to patients whose bodies can accept such treatment, or conversely, increase the risk of an adverse outcome for the patient. For example, the passage of the catheter through veins or arteries, especially through femoral arteries, can result in abrasions particularly at locations where the veins or arteries bend sharply on their way to the main coronary blood vessels. Further, once the catheter is inserted, the distal end of the catheter must be positioned exactly for accurate delivery of medication or other treatments via an extendible needle that is retracted during travel of the catheter to the final destination. There is a risk, in that once extended, the needle may scratch or perforate tissue by inadvertent or incorrect movement of the catheter tip. This is particularly problematic in applying an extendible needle to the right ventricle's wall, as it is quite thin and easily punctured. Any over-penetration or abrasion by the extendible needle or underlying catheter can cause bleeding and the formation of blood clots, which are potentially dangerous to the patient. To reduce the potential for clotting, the patient is frequently administered an anticoagulant such as heparin. While this precaution may reduce the chances of accidental blood clotting, it also creates a potential for uncontrolled bleeding internally, which is an equally dangerous situation to be avoided. What would be of great value to both patients and physicians is a device to deliver therapeutic or diagnostic agents, directly to a specific area within the heart, without the need for a blood thinner.
Targeted delivery of a gene therapy agent in a restricted region of the body can be used to modify cells in a desired region of the body. This technique, known as somatic gene therapy, is able to genetically express a therapeutically or diagnostically useful protein. Gene therapy can be a direct in vivo process in which genetic material is transferred to cells in the desired region of the patient's body. Alternatively, cells from the targeted region can be harvested, genetic material transferred to the cells, and the modified cells thereafter implanted back into the patient's body.
When using the direct in vivo method, a major concern is to avoid inserting the agent into a rapidly dividing cell population. This situation would substantially reduce the duration of the desired DNA transgene expression when using certain viral vectors such as the common adenovirus vectors. It is important, therefore, that the desired transgene or desired DNA is targeted so that, (1) only the desired cells will receive and express the gene, and (2) the gene will not be systemically distributed.
Currently, gene therapy for the heart muscle is still in the development stage. There have been studies of experimental gene therapy in rats by direct injection of DNA into the myocardium. The direct injection has caused inflammation, apparent myocyte necrosis, and scar tissue-formation along the needle tracks. Gene transfer using adenovirus vectors injected into pig hearts has been shown to be highly efficient in regions immediately adjacent to the injection, but evidence of gene transfer occurred only in a small region of the myocardium. A prominent inflammatory response has been associated with these injections, in part because current procedures utilizing catheters require that the catheter be inserted at the femoral artery. In order to overcome these difficulties, it is desirable to have the mechanism to insert a catheter into a body using an artery in an arm, such as a brachial artery or a radial artery. Catheter entry via an artery in the arm allows the patient the ability to walk immediately after an operation simply by keeping the pierced portion of the upper arm in an appropriately outstretched or elevated orientation. Moreover, injection through a brachial or radial artery eliminates potential abdominal-region pain. In order for a catheter to be administered through the brachial or radial artery, the catheter would have to be designed to accommodate the specific needs of subclavian insertion.
Direct injection catheters also may be used in treating disease of other parts of the body. They may be used for the treatment of peripheral vascular disease, which is due to insufficient blood flow to the legs. This procedure delivers recombinant adenovirus expressing an angiogenic peptide or protein to cells of the skeletal muscles via a catheter.
Thus, in spite of the interest in catheter-based treatments, there clearly still remain a number of important difficulties in effectively using this technique. The need for accurate positioning of the distal end of the catheter for delivery of the treatment medium is clear, but this is related to the ability to direct the distal end. Current catheter technology allows the bending of the near distal end in one direction only, thereby limiting the positionability of the tip. Another difficulty is in maintaining the distal end in contact with the tissue to receive treatment for the duration of the delivery activity. Too frequently, once positioned, the distal end moves, and in so doing, scratches or perforates the tissue to be treated thereby promoting bleeding. It is desirable also to effect the treatment delivery in as short a period of time as possible. Another limitation is the volume of liquid that can be passed through the lumen(s) at the distal end of the catheter. Simply pumping liquid at a higher pressure causes other problems because of the recoil of the catheter and hence movement away from the delivery site. It is, thus, highly desirable to provide a catheter capable of accurate positioning, one that allows the distal end to be anchored firmly against the tissue being treated, which can deliver the required quantity of one or more than one treatment agent rapidly but at low velocity, with minimal systemic loss, maintaining the agent in contact with the target tissue for the time required for treatment, which can be operated by a technician with minimal training, and requiring no special assisting technology. Such a catheter should eliminate the possibility of myocardial perforation and valve damage, even when applied to relatively thin wall thicknesses, such as the right ventricular wall.